The invention is based on a power tool, in particular a power sander, as generically defined by the preamble to claim 1.
In eccentric sanders and orbital sanders, it is known to use twoxe2x80x94pairedxe2x80x94ball bearings in line with one another to transmit a rotary motion or to generate an oscillating motion from a drive unit to a sanding plate.
This ball bearing, because of the structural design of such products, is always surrounded by abraded grinding material created during the work. This can happen because of air mixed with grinding material, or from turbulence in the region of the ball bearing.
Rotating masses create moments that twist an inner race and an outer race of the ball bearing counter to one another, so that a ball bearing seal between the inner race and the outer race lifts up and no longer performs its function. This creates a gap, which can allow grinding material to reach the interior of the ball bearing, and bearing lubricant can escape.
The invasion of grinding material and/or the escape of bearing lubricant between the ball bearing seal and the inner race or outer race of the ball bearing can lead to the destruction of the ball bearing and a failure of the eccentric sander or orbital sander. The resultant damage can be corrected only with what is usually an expensive repair.
Typically, to prevent tool failure, the intent is to prevent grinding material from being able to enter and mix with the bearing lubricant, which is accomplished by additionally using sealing disks, spin disks, and/or sealing rings.
The invention is based on a power tool, in particular a power sander with a housing and a motor, supported in the housing, that has a rotatable drive shaft which is connected operatively by one end to a tool, and in particular carries a sanding plate that can be equipped with grinding means, relative to which sanding plate the drive shaft is rotatably supported by means of a bearing, in particular by means of a roller bearing with an inner race and outer race spaced apart by a bearing gap and with rotationally fixed and rotatably disposed parts, and in particular is provided with means for removing grinding dust.
It is proposed that a bearing closely adjacent to any incident grinding dust and/or chips created has, on at least one side of its bearing gap, a plurality of sealing disks, in particular two of them, disposed side by side.
Instead of the single sealing disk that is usual at present, preferably at least two sealing disks per side are built into the bearing, preferably a roller bearing, with one sealing disk succeeding the other in the sealing gap. As a result of the sealing disks, a kind of labyrinth system can be achieved, and it can be reliably prevented that foreign substances will penetrate the bearing and/or that lubricants will escape. The positioning of the sealing disks can be done inside a component, in particular inside the outer race of a ball bearing. By means of the sealing disks, a sealing system can be achieved that is far more effective than a single sealing disk or than the combination of such a sealing disk with an additional seal. An undesired leakage gap from twisting of the outer race and inner race of the ball bearing relative to one another can be reliably prevented because of the attainable labyrinth effect. An advantageous labyrinth effect and a space-saving construction can be achieved in particular by means of closely adjacent sealing disks that preferably brace one another axially.
To minimize friction, toward the outside one grinding sealing disk and following it a contactless sealing disk can be used. With a contactless sealing disk in the axially inner region, it can also be achieved that lubricant that has penetrated between the sealing disks can flow back again. In principle, however, two or more grinding sealing disks or two or more contactless or non-grinding sealing disks each are also conceivable.
The proposed sealing system requires no further structural space outside the ball bearing, and an additional clamping of seals outside the bearing, and friction caused by an additional seal, can be avoided. By the use of the ball bearing with integrated sealing disks located one inside the other, only one component is required. Additional seals before and after the ball bearing can be avoided; the effort of assembly can be simplified; and additional errors from incorrect installation can be prevented. Furthermore, the sealing system is especially low in wear, since the sealing disks are encapsulated by the inner and outer races and are protected against external influences.
In order to achieve sealing disks that are advantageously as stiff as possible across the bearing gap, these sealing disks at least in part have a concave contour and/or have an inner metal part for reinforcement, preferably a zinc-coated sheet-metal part.
It is also proposed that the degree of filling of the bearing with lubricant is between 40% and 50%, and as a result a large reserve volume and a long service life can be attained.